Crystalline forms of imidoalkanpercarboxylic acids

ABSTRACT

Imidoalkancarboxylic acids of formula (I) are described, wherein A, X and M are as defined in the application, said acids being in a crystalline form which in contact with water gives rise to crystals having sizes lower than 30 micron.

The present invention relates to imido-alkan percarboxylic acids, havingan improved bleaching efficacy, usable also at a moderate temperature,even of the order from 10° C. to 30° C. for the industrial andcommercial applications in the detergency and disinfection.

More specifically the invention relates to a new crystalline form ofimido-alkanpercarboxylic acids, stable at the solid state but whensuspended in water, it is spontaneously transformed into crystals ofvarious crystalline form, stable in aqueous medium and having an averageparticle size lower than 30 micron, preferably lower than 8 micron, inparticular lower than or equal to 2 micron. The imido-alkanpercarboxylicacids obtained with said sizes have a higher bleaching efficacy, theconcentration being equal, with respect to those having sizes higherthan 30 micron and furthermore they can be formulated in dispersions,for example aqueous, for industrial and commercial applications by usingreduced amounts of chemical additive agents, in particular suspendingagents, with respect to those requested by the prior art.

It is known that imido-alkanpercarboxylic acids can be obtained forexample as slurries. They are known and used as bleaching agents indetergent formulations, or as main components of disinfectant oroxidizing compositions. The compositions containing said acids combinegood belaching properties with a good stability to storage.

The processes for the preparation of imido-alkanpercarboxylic acids arewell known in the literature and comprise the oxidation, in the presenceof a mixture of hydrogen peroxide and of a strong acid, of theimido-alkancarboxylic acid precursors. The precursor, in the case of thephthalimidoalkanpercarboxylic acids, is obtained by condensation ofphthalic anhydride, or phthalic acid with aminoacids or lactams, byreaction, optionally in the presence of water, at a pressure from 1 to30 bar and at temperatures ranging from 100° C. to 250° C., withreaction times from 1 to 20 hours. See for the example EP 325,289, EP325,288, EP 349,940. EP 490,409 describes a process to obtain with highyields percarboxylic acids wherein one operates in the presence ofparticular organic solvents for example CH₂Cl₂ and CHCl₃, by separatingat the end of the reaction the organic solvent containing thepercarboxylic acid from the aqueous phase containing sulphuric acid andhydrogen peroxide. The useful product is then recovered by removal ofthe organic solvent. In EP 560,155 various processes of the organicsolution treatment with water are described, by which for exampleε-phthalimido-peroxyhexanoic acid (PAP) as wet crystalline cake isfinally obtained, by filtration or centrifugation of aqueous slurriescontaining organic solvents, for example CH₂Cl₂ or ethyl acetate, withresidual water contents of the order of 20% by weight and traces ofresidual solvent in the range 50-2,500 ppm.

Generally the residual amounts of chlorinated solvents accepted in thealkanpercarboxylic acid formulations are very low. To lower the residualcontent of said chlorinated solvents in the obtained cake, as said, asubsequent purification treatment with a non chlorinated solvent forexample ethylacetate must be carried out, as described in EP 556,769.However the obtained alkanpercarboxylic acid contains not negligibleamounts of the solvent used in the last purification.

Furthermore, at the end of said treatments to lower the chlorinatedsolvent content by using the processes of the above patents, the waterpercentage by weight in the alkanpercarboxylic acid is of the order of20% or higher. This water amount is too high for the prepartion ofalkanpercarboxylic acid solid formulations and it is generally reducedby drying processes, which must be slow to avoid explosive peraciddecompositions. This is a critical phase of the industrial processes forobtaining peracids, due to its dangerousness and due to its poorproductivity. Besides with said drying processes a constant value of theresidual water content should be obtained, as required to carry out thefollowing working processes of the solid peracid.

EP 780,374 describes a process to reduce the water content ofimido-alkanpercarboxylic acids, initially higher than 12% by weight, toa constant value and lower than 10% by weight, said process comprisingthe heating steps of a suspension of an imido-alkanpercarboxylic acid inwater until the complete solid melting, subsequent separation of theorganic phase from the aqueous phase and recovery of the organic phasecontaining the imido-alkanpercarboxylic acid. The process of said patentis based on the fact that the pure imido-alkanpercarboxylic acids, forexample obtained by crystallization from organic solutions, have amelting point very close to the decomposition temperature; while theimido-alkanpercarboxylic acids in the presence of water are such to meltat a temperature significantly lower than the melting temperature, byforming eutectics. The water content constancy in the final peracid,typical of the eutectic composition, is a very important factor for thesubsequent product finishing treatments. The physical form of theperacid obtained with said process has the advantage to allow to avoidthe product granulation, which is carried out when the peracid is in thepowder form to make easier the subsequent operations during theformulation and/or transport.

It is known in the prior art that it is preferred the use in the bleachof crystalline peroxycarboxylic acids, obtainable as such in solid phaseand having a high title, and usable even in absence of hydrogenperoxide. Among them, sparingly water soluble peroxycarboxylic acids arepreferred, because they are more suitable for the development of notvery aggressive compositions for users, but effective in theseapplications already at room temperature. Among these sparingly watersoluble crystalline peroxycarboxylic acids, imido-alkanpercarboxylicacids are in particular known, for example ε-phthalimido-peroxyhexanoicacid (“PAP”) sold by Solvay Solexis (former Ausimont) by the trademarkEureco®. Said peracids are known from EP 325,288 and EP 325,289 in thename of the Applicant, as preferred for the production on an industrialscale and for the applications on commercial scale in the mentionedfields. For the detergency use see in particular the compositions ofsaid peracids described in EP 852,259 in the name of the Applicant. Forthe uses in the fields of the body care, of the cosmetics andpharmaceutics, see the compositions described in EP 895,777, EP1,074,607 in the name of the Applicant.

The ε-phthalimido-peroxyhexanoic acid (“PAP”) is particularly preferredin the above application fields for its exceptional stability incrystalline solid phase and for the consequent safety with which it canbe handled and used on a large scale. The exceptional thermal stabilityof the PAP in crystalline form, also at the solid state of technicaldegree, obtained both by experimental laboratory processes and byindustrial processes, is known in the prior art and distinguishes itfrom most of the known crystalline peroxycarboxylic acids, see forexample EP 490,409 in the name of the Applicant. This higher PAPchemico-physical stability is lower when the PAP is present under thesolute form in a solution of a chemically compatible and inert solvent,for example water, within the solubility limits set by the solutiontemperature. A contribution to the exceptional PAP stability at thesolid state seems therefore to derive from the nature itself of itscrystalline form known in the prior art, since easily obtainable by PAPcrystallization from its solutions in organic solvents, for example asdescribed in the already mentioned patents EP 556,769 and EP 560,155, oralso by PAP solidification from one of its melted phase of eutecticcomposition, in the presence of water, see EP 780,374. In all said casesthe obtained PAP crystals have on an average sizes higher than 100micron. The imido-alkanpecarboxylic acids in the known crystalline formare not obtainable by crystallization from an aqueous solution, owing totheir low solubility in water. An useful implication for the practicalpurposes of this property of imido-alkanpercarboxylic acids is thesubstantial stability in the time of the aqueous crystal dispersions ofsaid peracids, which do not show phenomena of morphological modificationby spontaneous recrystallization. Therefore said aqueous dispersionsmaintain their chemico-physical characteristics even for long storagetimes.

It is also known that the performances of the formulations based onsparingly water soluble crystalline imido-alkanpercarboxylic acids,especially in the applications at low temperature, are more effectiveand suitable if the peracid in crystalline phase is present under theform of particles having sizes on an average lower than 100 micron. Inthis case indeed in the application phase the bleach action takes placewithout undesired phenomena, as the presence of solid residues ontreated tissues or a local colour fading or a located damage of the lessresistant fibers. See for example patent application WO 00/27,960. Saidparticles having on an average sizes lower than 100 micron can beobtained by two milling operations in series starting from crystalsobtained by the processes of the prior art. It is known indeed that tohave a more effective milling to obtain particles having on an averagesizes lower than 100 micron, subsequent millings must be appliedutilizing techniques having a complementary effect. See patentapplication WO 00/27,969. With said particular milling technologies itis possible to obtain formulations of imido-alkanpercarboxylic acidswherein the peroxyacid is present in a stable form under the form ofparticles having sizes on an average lower than 100 micron. Testscarried out by the Applicant have shown that said sizes can be reducedto sizes on an average of 35 micron. See the comparative Examples. Thedrawback of said milling technologies is that mills for milling arerequired involving significant investment and working, maintenance andprocess and quality control costs. Furthermore said technologies implyadditional costs for the use of specific chemical additives to makemilling easier, and for the maintenance in the time of the so obtainedmicroscopic particles of the imido-alkanpercarboxylic acids. Indeed inabsence of said additives the particles would tend to aggregate again.The use of said specific additives makes easier the hard milling of saidperacids reducing the mechanical stress to which said crystallineperacids are subjected. In practice said additives allow to obtainparticles of said peracids having on an average sizes lower than 100micron, even to 35 micron and in a stable physical form in the time.

It is known, furthermore, see patent application WO 00/27,982, that thepurity of imido-alkanpercarboxylic acids in the compositions must behigh and the residual impurities in said peracids must be lower than 5%by weight. Furthermore pollutants must be absent since couldaccidentally enter the composition during the composition and millingprocesses and which negatively influence the duration in the time andthe intrinsic safety of said compositions, in particular of those havinga high content of imido-alkanpercarboxylic acids. When milling is used,the use of a peracid originally having a high purity and of accurateworking techniques allow in the industrial practice to obtain peracidparticles having on an average sizes of the order of 35 micron andchemically stable in the time.

It is also known that in the case of compositions ofimido-alkanpercarboxylic acids finely dispersed in aqueous phase, theselection of effective suspending agents, capable to assure in the timethe desired chemico-physical stability of the system and the constancyof its Theological properties, is critical. To obtain these propertiesthe concentration of said suspending agents is not reducible beyondcertain values, and their cost results not negligible compared with thattotal of the composition. See for example EP 1,074,607.

The need was felt to have available imido-alkanpercarboxylic acids in aphysical form such to assure an improved bleaching efficacy and indisinfection allowing the use of said peracids also at temperatures of10° C.-30° C. in detergency and in disinfection, without making use ofthe milling technologies and the additives required for milling asdescribed in the prior art, said imido-alkanpercarboxylic acids beingcapable to give compositions wherein the used amount of suspendingagents was lower than that of the compositions of the prior art, evenmaintaining the same chemico-physical stability and the constancy of therheological properties in the time.

The Applicant has unexpectedly and surprisingly foundimido-alkanpercarboxylic acids allowing to solve the above technicalproblem.

An object of the present invention are imido-alkanpercarboxylic acidshaving formula (I):

wherein A indicates a group selected from the following:

wherein:

-   -   n is an integer 0, 1 or 2,    -   R1 has one of the following meanings: hydrogen, chlorine,        bromine, C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, aryl or alkylaryl,    -   R2 is hydrogen, chlorine, bromine or a group selected from the        following: —SO₃M, —CO₂M, —CO₃M or —OSO₃M,    -   M has the meaning of hydrogen, an ammonium alkaline metal, or an        equivalent of an alkaline-earth metal,    -   X indicates a C₁-C₁₉ alkylene or arylene;        said imido-alkanpercarboxylic acids being in a crystalline form,        herein called alpha, stable at storage at the solid state, and        when dispersed in water it is transformed into crystals of the        known crystalline form of the prior art (herein called beta),        stable in aqueous environment, said novel crystals of beta        crystalline form having average sizes lower than 30 micron,        preferably lower than 10 micron, more preferably lower than 8        micron, particularly lower than or equal to 2 micron; the alpha        crystalline form being characterized with respect to the known        beta crystalline form of the prior art in that the respective        spectra obtained by the X Ray Diffraction and the Surface        Infrared Spectroscopy (IR/S) techniques show, with respect to        those of the beta form of the same peracid, a different spectral        imagine at X rays and a typical absorption shift in the        1697-1707 cm⁻¹ zone at IR/S towards higher frequencies, of the        order of about 8-10 cm⁻¹.

The crystals of the alpha form have the same solubility in water of thecrystals of the prior art (beta form). Therefore they form aqueousdispersions.

In particular in the case of the ε-phthalimido-peroxyhexanoic acid (PAP)the beta form known in the prior art shows:

-   -   at X rays: typical peaks at 18.0 and 18.7 and no quadruplet at        24.2-25.0 [°2θ],    -   at the IR/S spectrum: typical peak with maximum absorption in        the 1699-1704 cm⁻¹ zone, for dried crystals having water        absorption at 3450-3500 cm-¹ lower than 5%;        while, for the same PAP compound the alpha form shows the        following spectral characteristics:    -   at X rays: typical peaks at 17.5 and 19.0 and typical quadruplet        at 24.2-25.0 [°2θ],    -   at IR/S spectrum: typical peak with maximum absorption in the        1707-1712 cm⁻¹ zone for dried crystals, having a water        absorption at 3450-3500 cm⁻¹ lower than 5%.

The X ray spectrum is carried out on dried powder samples for 48 h at20° C. under vacuum (residual pressure 10 mmHg).

Said alpha crystalline form is therefore distinguishable from the knownbeta crystalline form of the prior art of the sameimido-alkanpercarboxylic acids both by the above characterizationmethods, and mainly due to the fact that suspended in water it isspontaneously transformed into stable crystals of different form (beta),stable in water and having sizes on an average lower than 30 micron,preferably lower than 10 micron, more preferably lower than 8 micron andin particular of the order of 2 micron.

The crystal sizes of alpha form are not critical for the obtaining ofcrystals of the beta form having the above mentioned sizes.

The imido-alkanpercarboxylic acids in alpha crystalline form can beformulated in solid compositions, for example granulated with thetechniques used in the prior art for crystals of beta type for their usein the detergency and disinfection field. See for example EP 852,259,herein incorporated by reference.

A further object of the present invention are imido-alkanpercarboxylicacids of beta crystalline form, obtainable by dispersing in watercrystalline particles of the corresponding alpha form, said particles ofbeta crystalline form having average sizes lower than 30 micron,preferably lower than 10 micron, more preferably lower than 8 micron, inparticular lower than or equal to 2 micron.

A further object of the present invention are compositions ofimido-alkanpercarboxylic acids, in particular in aqueous phasecompositions, containing said peracids under the form of betacrystalline particles having sizes, on an average, lower than 30 micron,preferably lower than 10 micron, more preferably lower than 8 micron, inparticular lower than or equal to 2 micron, obtained by treating thecorresponding alpha form of the peracid, as mentioned above.

The peracid concentration in the beta form, having sizes lower thanthose of the prior art, in said compositions ranges from 0.5% to 25%,expressed in per cent by weight based on the total of the composition.

As said, the beta form crystals are stable both in aqueous dispersionand at the solid state. It has been surprisingly and unexpectedly foundby the Applicant that the crystals in beta form, having the above sizes,can be formulated even in aqueous phase using very reduced amounts ofsuspending agents, even less than ⅕ by weight with respect to those usedto prepare the commercial compositions having an aqueous base containingimido-alkanpercarboxylic acids obtained by the milling techniques of theprior art.

In particular it is possible to use suspending additives, for examplepolymers as xanthan rubber, at concentrations, expressed in percentagesby weight from 0.05% to 0.1% based on the total of the composition,instead of the usual concentrations of 0.40-0.60% by weight.

The amount of suspending additives which can be used in saidcompositions, expressed in percentages by weight on the total of thecomposition is from 0.05% to 0.6%, preferably from 0.05% to 0.1%.

Besides, to the invention compositions the other conventional additives,for example surfactants, preferably selected from those nonionic and/oranionic, in the usual concentrations useful for the final productperformances, can be added.

Optionally it is possible to add to said compositions hydrogen peroxideat concentrations, expressed in percentages by weight, from 0 to 10%based on the total of the composition.

The compositions obtained from said imido-alkanpercarboxylic acids, inthe crystalline sizes of beta form on an average lower than 30 micron,result stable in the time from the chemical and physical point of view.

Said compositions are advantageously usable in the bleach anddisinfection field with lower costs and performaces higher than thoseobtainable with the known compositions of the prior art, in particularfor the applications at room temperature and at low temperatures. Assaid, the amount of suspending additives in said compositions is lowerthan that used in the compositions of the known imido-alkanpercarboxylicacids of the prior art.

The beta crystalline imido-alkanpercarboxylic acids of the presentinvention having the average particle sizes in the above limits, areobtainable by an advantageous process, feasible on a large scale, safeand not very expensive, wherein milling additives are not used, thusavoiding potential pollutions of the imido-alkanpercarboxylic acids.

In said process particles of the imido-alkanpercarboxylic acid in alphaform, stable at the solid state but unstable in aqueous dispersion, arefirst obtained, then transformed, as described, into the stable betaform.

To obtain the imido-alkanperoxycarboxylic acids of formula (I) in thebeta crystalline form, having the above sizes, the peracid particles inthe alpha form are suspended in a stirred aqueous phase and maintainedat temperatures from 0° C. to 70° C., preferably from 20° C. to 65° C.,more preferably from 40° C. to 60° C., for a time ranging from 1 minuteto 90 minutes, preferably from 10 minutes to 60 minutes, more preferablyfrom 20 minutes to 45 minutes.

A further object of the present invention is a process for thepreparation of imido-alkanperoxycarboxylic acids of formula (I) havingparticles in the alpha crystalline form, said process comprising thefollowing steps:

-   I) peroxidation in the presence of hydrogen peroxide and of a strong    acid generally at temperatures comprised between 5° C. and 50° C.,    of an imido-alkancarboxylic acid precursor obtainable by reaction    of:    -   a) an anhydride of formula:

-   -    or its corresponding acids, A being as above, with    -   b1) an aminoacid of formula:

-   -    X being as above, or    -   b2) a lactam of general formula:

-   -    Y having the meanings of X, preferably a C₃-C₁₉ alkylene;    -   c) water;    -   at temperatures in the range 100° C.-250° C., under pressure of        an inert gas from 1 to 30 bar (0.1-3 MPa), for reaction times        from 1 to 20 hours;

-   II) obtaining of a melted phase of eutectic composition of the    imido-alkanperoxycarboxylic acids of formula (I) by heating a    suspension in water of said peracids until the complete solid    melting, said eutectic having a composition on a molar basis of no    more than two moles of water/peracid mole;

-   III) separation from the melted organic phase of eutectic    composition from the balanced aqueous phase, and recovery of the    melted organic phase containing the imido-alkanpercarboxylic acid;

-   IV) quench of the melted organic phase and obtaining of the phase    called herein alfa, stable at the solid state (but unstable at    contact with water), as above.

Said quench of step IV) of the process can be carried out in variousways. For example by dripping the melted organic phase of eutecticcomposition in liquid nitrogen. Another quench method is for example thedripping in cold water, under stirring, having a temperature for examplelower than 15° C. To obtain only the alpha form, the skilled man of thefield is easily able to determine the most suitable temperature, keepingin mind that as the temperature increases, the beta form can becontemporaneously obtained together with the alpha form. Another quenchmethod is the percolation of the melted phase on one, for example metal,surface or on two, for example metal, surfaces coupled and cooled attemperatures lower than 30° C.

In step I) the ratio by moles generally between a/(b1 or b2)/c is in therange 1/0.8:1.2/0.5:3. Preferably the ratio by moles a/(b1 or b2)/c iscomprised between 1/1.01:1.1/0.5:2.5, more preferably between1/1.05:1.1/1-2.

In step I) it is preferred to react the anhydride a), or thecorresponding acid, with the lactam b2).

Among the compounds of class a1) the following anhydrides or thecorresponding acids can be mentioned: succinic, glutaric, maleic,trimellitic, phthalic, pyromellitic and alkyl- or alkenyl-succinicanhydride. Preferably the phthalic anhydride or the phthalic acid areused.

Among the class b1) compounds the following can be mentioned:omega-aminobutyric, omega-aminovalerianic, omega-aminocaproic andomega-aminolauric acids.

Among the compounds of class b2) it can be mentioned as preferred:gamma-pyrrolidone, delta-piperidone, epsilon-caprolactam andomega-laurolactam, epsilon-caprolactam (CPL) is particularly preferred.

Preferably in step I) the temperature is in the range 130° C.-180° C.and the pressure between 4 and 8 bar.

At the end of step I) a solvent, preferably CH₂Cl₂ and CHCl₃, morepreferably CH₂Cl₂, is preferably added to make easier the subsequentperoxidation of the product.

The last solvents indeed, as described in the patent application EP780,373 in the name of the Applicant, are the most suitable to carry outthe successive peroxidation operation.

Among imido-alkanpercarboxylic acids it can be mentioned thephthalimido-peracetic acid, ε-phthalimido peroxyhexanoic acid,3-phthalimido-perpropionic acid, 4-phthalimido-perbutyric acid,2-phthalimido-diperglutaric acid, 2-phthalimido-dipersuccinic acid,3-phthalimido-perbutyric acid, 2-phthalimido-perpropionic acid,3-phthalimido-diperadipic acid, naphthalimido-peracetic acid,2-phthalimido-monopersuccinic acid.

In step II) to reduce the amount of water, sequestrants can be added inthe aqueous phase. For example there can be mentioned hydroxycarboxylicacids, as citric acid; amino-policarboxylic acids, asethylendiaminotetramethylphosphonic acid (EDTMP); pyridincarboxylicacids, such as dipicolinic acid; polyphosphonic acids, for example1-hydroxy-ethyliden-1,1-diphosphonic acid (HEDP).

Crystalline imido-alkanperoxycarboxylic acids of alpha form obtained bythe above process, are stable at the solid state, as said and theyclearly distinguish themselves from the same crystalline acids in betaform since they are spontaneously transformed into the correspondingmicrocrystals of beta form by mere contact with an aqueous phase.

As said, the so obtained crystals of imido-alkanperoxycarboxylic acidsof beta form distinguish themselves from those obtained by the knownmethods of the prior art (milling) by the improved bleaching propertiesand the lower amount of chemical additives necessary for the preparationof the corresponding compositions. The imido-alkanperoxycarboxylic acidcrystals of beta form of the invention have on an average sizes clearlylower than those obtainable by the known milling methods of the priorart.

Said microcrystals in beta form obtained by the invention process fromcrystalline imido-alkanperoxycarboxylic acids in alpha form, besides thespecific bleach activity, are more effective than the crystals obtainedaccording to the methods of the prior art also in terms of antibacterialand disinfectant activity, especially in the applications at roomtemperature (15° C.-25° C.) or at lower temperatures.

As said, the microcrystals of the imido-alkanperoxycarboxylic acids inbeta form of the invention are of particular interest since they requirelower amounts of chemical additives for obtaining compositions ofcommercial interest stable in the time. Furthermore they do not needchemical process auxiliary agents as described in the prior art for thefine milling of crystalline imido-alkanperoxycarboxylic acids. Besides,they can be obtained also on an industrial scale with simplifiedprocesses and with reduced investment and working costs.

The imido-alkanperoxycarboxylic acids in the invention alpha crystallineform are stable in the time, even in case of prolonged storage, andsubjected to the above described process they are spontaneouslytransformed into microcrystals of beta form, having the above averagesizes and the desired characteristics for the preparation ofcompositions, as above described.

The following Examples illustrate with non limitative purposes theinvention.

EXAMPLE 1A

PAP Preparation Having Alpha Crystalline Form by Mass-crystallization

100 ml of demineralized water “Micropure Grade” and 0.5 g ofhydroxyethyliden-diphosphonic acid (HEDP) (Supplier Bozzetto: HEDP10H60), are introduced in a 200 ml jacketed beaker equipped with anoutlet valve on the bottom and the solution is heated up to about 78° C.Then 100 g of crystalline PAP of technical degree (Ausimont, Eureco® Wtype) are added. It is put under stirring at the rate of about 250 rpmand the PAP melting is expected, which takes place when the systemtemperature rises again to a value of about 78° C. At this temperaturethe two formed liquid phases, respectively the organic phase formed bythe PAP eutectic with water and the aqueous phase, result transparent.The stirring is reduced to 20 rpm and the evident separation of the twophases with the heavier organic phase which gathers on the bottom isobtained.

About 250 ml of liquid nitrogen are drawn in a Dewar vessel, and amagnetic anchor is immersed therein to stir the liquid with a magneticstirrer, positioning this vessel immediately under the outlet valve ofthe jacketed beaker containing on the bottom the melted organic phase.

The bottom valve of this is slowly opened and the melted liquid is letdrip in the liquid nitrogen phase. The operation is interrupted as soonas the upper level of the melted organic phase in the jacketed beakerapproaches the bottom valve. The solidified PAP is separated from thestill liquid nitrogen, taking the solid with a round spatula, andtransferring it into a small plastic tank resistant to low temperatures.

After having conditioned again the product at the room temperature, thePAP granules are dried by drying under vacuum, at about residual 10mmHg, at a temperature not higher than 20° C. The specimen, weighingabout 70 g of crystalline PAP is characterized by the X Ray Diffractionand Surface Infrared Spectroscopy (IR/S) techniques. The obtainedspectra identify the alpha form.

-   X Rays: typical peaks at 17.5 and 19.0 and typical quadruplet at    24.2-25.0 [°2θ].-   IR/S: typical peak with maximum absorption in the 1707-1712 cm⁻¹    zone (anhydrous crystals: absorption at 3450-3500 lower than 5%).

EXAMPLE 1B (COMPARATIVE)

PAP Preparation of Beta Crystalline Form (Crystalline Form of the PriorArt) by Mass-crystallization

By initially operating according to the procedure of Example 1A, themelted organic phase formed by the PAP eutectic with water is fed to abeaker containing water at the temperature of about 40° C., and keptunder stirring with a magnetic stirrer and a magnetic anchor. After themelt solidification, the solid separation from the liquid, the granularproduct is dried with the same method described to remove the residualwater in Example 1A. Also this specimen is characterized by the X RayDiffraction and the Surface Infrared Spectroscopy techniques. Theobtained spectra identify the beta form.

-   X Rays: typical peaks at 18.0 and 18.7 and no typical quadruplet at    24.2-25.0 [°2θ].-   IR/S: typical peak with maximum absorption in the 1699-1704 cm⁻¹    zone (anhydrous crystals: absorption at 3450-3500 lower than 5%).

EXAMPLE 1C (COMPARATIVE)

Example 1B has been repeated but by using water cooled at 15° C. Theresults are equal to those obtained in Example 1B.

EXAMPLE 2A

PAP Preparation of Beta Microcrystalline Form Starting from PAP of AlphaCrystalline Form

In a beaker immersed in a thermostatic bath an aqueous dispersion ofalpha crystalline PAP in demineralized water at 5% by weight of PAP isprepared, by adding to 473.5 ml of demineralized water at thetemperature of 50° C., kept under stirring with an anchor and a magneticstirrer, 500 ppm of antifoam DB 100 and 1,000 ppm of surfactantHostapur® SAS and 26.50 g of crystalline PAP in alpha form, of technicaldegree (titre: 94.3%) having average sizes higher than 100 micron. After10 minutes of stirring at 50° C., the beaker is removed from thethermostatic bath and the aqueous suspension is transferred in agraduated cylinder. It is let rest at room temperature in the graduatedcylinder. In the suspension no thickenining of solid phase on thecylinder bottom is observed, both after two hours and after 48 hours,and a separation of supernatant clear liquid phase of no more than 20%by volume even after 10 days is noticed.

One sample of said aqueous dispersion, observed with optical microscope(50 and 500 magnifications) shows that the PAP crystals dispersed in thewater have average sizes lower than 10 micron, in particular lower than2 micron. These microcrystals, recovered and studied by means of theanalytical techniques of Example 1, show the same characteristics ofbeta form crystals and no longer those of the starting alpha formcrystals.

EXAMPLE 2B (COMPARATIVE)

Repetition of Example 2A but by Starting from Crystalline PAP in BetaForm.

An aqueous dispersion of crystalline PAP in demineralized water at 5% byweight of PAP is prepared, as described in Example 2A, by adding to471.9 ml of demineralized water 500 ppm of antifoam DB 100 and 1000 ppmof surfactant Hostapur® SAS and 28.1 g of crystalline PAP in beta formof technical degree (titre: 89%), having average sizes higher than 100micron, in particular 80% of the particles being comprised between 100and 200 micron. After 10 minutes of stirring at 50° C., the beaker isremoved and the suspension is transferred into a graduated cylinder, asin Example 2A. Already after 10 minutes rest at room temperature in thegraduated cylinder, it is observed the clear separation of a supernatantaqueous phase for 60% of the total volume and the sedimentation of aprecipitate on the bottom. The separation of the supernatant aqueousphase increases after 2 hours to more than 70% of the total volume.

A solid specimen, examined by optical microscope and by the techniquesmentioned in Example 1A, shows that the crystals have unchanged sizesand properties with respect to those of the starting PAP crystals inbeta form.

EXAMPLE 3

Dissolution Rate of PAP Crystals of Beta Form, and of PAP Microcrystalsof Beta Form Obtained from PAP Crystals of Alpha Form According toExample 2A

A test is carried out for the determination of the dissolution time, bydispersing 100 mg of anhydrous crystalline PAP (base 100%), respectivelyof crystals and microcrystals (sizes lower than 10 micron) of PAP inbeta form, obtained as from Examples 2B and 2A respectively, in onelitre of solution prepared with water having a 10° F. hardness and 1.70g of standard detergent base, free from bleach aditives (detergent IECtype B, with phosphates—Publication IEC 60,456), kept under stirring andthermostated at the temperature of 40° C.

Successive samples of liquid phase, carefully filtered on filter of 0.45micron, are drawn and the PAP concentration in solution is determined byHPLC.

The necessary times for the dissolution of 90% of the crystalline PAPinitially dispersed in the aqueous solution are of 30 and 15 minutesrespectively for the used crystals and microcrystals of PAP in betaform.

Said times are determined by drawing some curves reporting in ordinatethe PAP concentration dissolved in the aqueous phase (determined byHPLC) and in abscissae the sample drawing time, taking as 100% the PAPconcentration asymptotically obtained at infinite time.

The previous test is repeated by dispersing 70 mg of anhydrouscrystalline PAP (base 100%), respectively of crystals and microcrystals(sizes lower than 10 micron) of PAP in beta form, obtained as fromExamples 2B and 2A respectively, in one litre of aqueous solution,prepared as above, stirred and thermostated at the temperature of 25° C.

Successive samples of liquid phase, carefully filtered on filter of 0.45micron, are drawn, and the PAP concentration in solution is determinedby HPLC.

The necessary times for the dissolution of 90% of the crystalline PAPinitially dispersed in the aqueous solution are of 60 and 14 minutesrespectively for the used crystals and microcrystals of PAP in betaform.

EXAMPLE 4A (COMPARATIVE)

Preparation of a Typical PAP Composition Having an Aqueous Basis andEvaluation of the Respective Bleach Activity

A typical composition having an aqueous basis at 10% by weight of activePAP is prepared with crystalline PAP in beta form, milling it by acolloid mill and subsequently by a high flow rate mill with impact andcavitation and adding then, under stirring for 30 minutes at thetemperature of 45° C., the following substances in the indicatedamounts, expressed in percentages by weight on the final composition:

-   -   non-ionic surfactant 2.5%,    -   xanthan rubber 0.50%,    -   HEDP 0.1%.

The obtained dispersion is chemically and physically stable even afterexposure at the temperature of 35° C. in a stove for 7 days. The initialviscosity of 670 mpa.s becomes 730 mpa.s after 7 days at 35° C.

The bleach activity of said composition is evaulated according to alaboratory test, by treatments in combination with HD detergent (HeavyDuty) at 40° C. for 30 minutes, or in combination with LD detergent at30° C. (Light Duty) for 30 minutes, of a set of test cotton tissuesdirtied with the following types of artificial dirt EMPA: art. 114 (redwine), art. 167 (tea) and art. 164 (grass), obtaining a white degree of70, 67.5 and 63 (HD detergent), or of 72, 73 and 64.5 (LD detergent)respectively.

EXAMPLE 4B

Repetition of Example 4A Using Crystalline PAP in Alpha Form

The same standard composition having an aqueous basis at 10% by weightof active PAP is prepared with crystalline PAP in alpha form. Crystalsare milled for 5 minutes with Brown® Minipimer mill and, by maintainingunder stirring for 30 minutes at the temperature of 45° C., thefollowing substances are added in the indicated amounts, expressed inpercentages by weight on the final composition:

-   -   non ionic surfactant 2.5%,    -   xanthan rubber 0.10%,    -   HEDP 0.10%.

The obtained dispersion is chemically and physically stable, even afterexposure at the temperature of 35° C. in a stove for 7 days. The initialviscosity of 570 mPa.s becomes 580 mPa.s after 7 days at 35° C.

The bleach activity of this formulation is evaluated by using the sameabove mentioned laboratory test, by treatments in combination with HDdetergent at 40° C. for 30 minutes, or in combination with LD detergentat 30° C. for 30 minutes, of a set of test cotton tissues dirtied withthe following types of artificial dirt EMPA: art. 114 (red wine), art.167 (tea) and art. 164 (grass), obtaining a bleach degree of 71, 69.5and 63 (HD detergent), or 73, 73.5 and 65.5 (LD detergent) respectively.

EXAMPLE 5

Dissolution Rate of the Crystalline PAP in Beta Form Present in LiquidCompositions Having an Aqueous Basis

Three compositions having an aqueous basis of commercial interest calledrespectively A, B, C, containing in suspension PAP crystals in beta formare prepared and the PAP dissolution times thereof are determined by themethods described in Example 3, by dispersing a sample of the singlecomposition to be tested in 1 litre of solution, prepared with waterhaving a 10° F. hardness, and 1.70 g of standard detergent base ofExample 3, at the temperature of 25° C.

The three compositions A, B and C subjected to the test are respectivelyobtained as follows:

-   -   Formulation A:        -   60 g of PAP of alpha form of technical degree,        -   1.50 g of xanthan rubber,        -   10 g of non ionic surfactant,        -   0.6 g of antifoam DB100        -   are dispersed in 928 g of water at 50° C. and treated for 5            minutes by Silverson equipment, then with blade mechanical            stirrer for 30 minutes at 50° C. and subsequently for 30            minutes at room temperature.        -   The obtained composition A has a titre in active PAP of            5.02% and a viscosity at 25° C. of 120 mPa.s. The PAP            crystals dispersed in the aqueous phase have sizes lower            than 10 micron.    -   Formulation B:        -   60 g of PAP of alpha form of technical degree,        -   1.0 g of xanthan rubber,        -   3.4 g of anionic surfactant Hostapur®SAS,        -   0.6 g of antifoam DB100    -   are dispersed in 935 g of water at 50° C. and treated for 5        minutes with Silverson equipment, then with blade mechanical        stirrer for 30 minutes at 50° C. and subsequently for 30 minutes        at room temperature.        -   The obtained composition B has a titre in active PAP of 5.0%            and a viscosity at 25° C. of 300 mPa.s. The PAP crystals            dispersed in the aqueous phase have sizes lower than 2            micron.

The composition C is the same comparative composition described inExample 4A.

With the test to determine the dissolution times at 25° C. of thecrystalline PAP contained in the three compositions A, B and C, thevalues reported in Table 2 are obtained, wherein T_(98.0), T_(99.0) andT_(99.8) show the necessary times for the dissolution respectively of98.0%, 99.0% and 99.8% of the PAP initially introduced in the testsolution.

Said times and respective percentages are determined as described inExample 3.

From the Table it results that the time necessary for the PAPdissolution of the compositions A and B is undoubtedly lower than thetime requested by the composition C of the prior art.

TABLE 1 Examples 4A comp. and 4B: comparison between the results (whitedegree) obtained in the washing tests using mixtures containing HDdetergent, or respectively LD, and compositions formed by (% by weight):2.5% of non ionic surfactant, 0.10% HEDP, and respectively the % ofxanthan rubber and 10% of PAP of the type as indicated in the Table Ex.4A Comp Ex. 4B PAP and xanthan rubber in the composition PAP beta alphaxanthan rubber (% by weight) 0.5 0.1 Washing tests Composition + HDsurfactant White degree: art. 114 (red wine) 70 71 art. 167 (tea) 67.569.5 art. 164 (grass) 63 63 Washing tests Composition + LD surfactantWhite degree: art. 114 (red wine) 72 73 art. 167 (tea) 73 73.5 art. 164(grass) 64.5 65.5

TABLE 2 Example 5, dissolution rate of the crystalline PAP present inthe liquid compositions having an aqueous basis A, B and C. T_(98.0)T_(99.0) T_(99.8) Compositions min min min A <5 7 20 B <<5 <5 10 C 5 1565 T_(98.0), T_(99.0) and T_(99.8) show the times necessary for thedissolution respectively of 98.0%, 99.0% and 99.8% of the PAP initiallyintroduced in the test solution.

1. An imido-alkanpercarboxylic acid represented by formula (I):

wherein A is

wherein: R1 is hydrogen, chlorine, bromine, C₁-C₂₀ alkyl, C₂-C₂₀alkenyl, aryl, or alkylaryl, R2 is hydrogen, chlorine, bromine —SO₃M,—CO₂M, —CO₃M or —OSO₃M, M is hydrogen, an ammonium alkaline metal, or analkaline-earth metal equivalent, and X is a C₁-C₁₉ alkylene or anarylene; wherein said imido-alkanpercarboxylic acid is in a crystallineform of alpha that is stable at storage at the solid state, but whendispersed in water is capable of being transformed into one or morecrystals of beta crystalline form that are stable in aqueousenvironment, wherein said one or more crystals of beta crystalline formhave an average size of lower than 30 microns, and wherein therespective spectra of the alpha crystalline form obtained by X-rayDiffraction and Surface Infrared Spectroscopy techniques show, withrespect to the spectra of the beta form of the same peracid, exhibit adifferent spectral X-ray image and a typical absorption shift in the1697-1707 cm⁻¹ zone by Surface Infrared Spectroscopy towards higherfrequencies, of the order of 10 cm⁻¹.
 2. The imido-alkanpercarboxylicacid according to claim 1, wherein the acid isε-phthalimido-peroxyhexanoic acid in alpha crystalline form, and has thefollowing chemico-physical parameters: X-ray spectrum showing peaks at2θ=17.5° and 19.0° and quadruplet at 2θ=24.2°-25.0°, and SurfaceInfrared Spectroscopy spectrum showing a peak with maximum absorption inthe 1707-1712 cm⁻¹ zone, for an anhydrous crystal, having a waterabsorption at 3450-3500 cm⁻¹ lower than 5%.
 3. A process for thepreparation of said imido-alkanperoxycarboxylic acid of claim 1, saidprocess comprising: I) peroxidating, in the presence of hydrogenperoxide and of a strong acid at a temperature of between 5° C.-50° C.,an imido-alkancarboxylic acid precursor obtained by reacting: a) ananhydride represented by formula (II):

or the corresponding acid, with b1) an aminoacid represented by formula(III):

or b2) a lactam represented by formula (IV):

Y having the meanings of X; and c) water; at temperatures in the range1000° C.-2500° C., under pressure of an inert gas from 1 to 30 bar, fora reaction time of from 2 to 20 hours; II) obtaining of a melted phaseof eutectic composition of said imido-alkanperoxycarboxylic acid offormula (I) by heating a suspension in water of saidimido-alkanperoxycarboxylic acid until the complete melting of thesolid, said eutectic having a composition on a molar basis of no morethan two moles of water/imido-alkanpercarboxylic acid; III) separatingsaid melted organic phase of eutectic composition from the aqueous phasein balance and recovering a melted organic phase comprising saidimido-alkanpercarboxylic acid; IV) quenching said melted organic phaseto obtain said crystalline form of alpha, stable at the solid state. 4.The process according to claim 3, wherein said quenching is carried outby dripping said melted organic phase of eutectic composition in liquidnitrogen.
 5. The process according to claim 3, wherein said quenching iscarried out by dripping said melted organic phase of eutecticcomposition in cold water, under stirring, having a temperature lowerthan 15° C.
 6. The process according to claim 3, wherein said quenchingis carried out by percolating said melted organic phase on a metalsurface, or on two metal surfaces, coupled and cooled at temperatureslower than 30° C.
 7. The process according to claim 3, wherein in stepI) the ratio by moles between a/(b1 or b2)/c is in the range1/0.8-:1.2/0.5:3.
 8. The process according to claim 3, wherein in stepI) the anhydride a) or said corresponding acid is reacted with saidlactam b2).
 9. The process according to claim 3, wherein said anhydrideor said corresponding acid is selected from the group consisting of:succinic, glutaric, maleic, trimellitic, phthalic, pyromellitic,alkyl-succinic, and alkenyl-succinic anhydride.
 10. The processaccording to claim 3, wherein said amino acid is selected from the groupconsisting of: omega-aminobutyric, omega-aminovalerianic,omega-aminocaproic and omega-aminolauric acid.
 11. The process accordingto claim 3, wherein said lactam is selected from the group consistingof: gamma-pyrrolidone, delta-piperidone, epsilon-caprolactam, andomega-laurolactam.
 12. The process according to claim 3, wherein in stepI) the temperature is in the range 130° C.-180° C. and the pressure isin the range 4-8 bar.
 13. The process according to claim 3, wherein saidimido-alkanpercarboxylic acid is selected from the group consisting ofphthalimido-peracetic acid, ε-phthalimido peroxyhexanoic acid,3-phthalimido-perpropionic acid, 4-phthalimido-perbutyric acid,2-phthalimido-diperglutaric acid, 2-phthalimido-dipersuccinic acid,3-phthalimido-perbutyric acid, 2-phthalimido-perpropionic acid,3-phthalimido-diperadipic acid, naphthalimido-peracetic acid,2-phthalimido-monopersuccinic acid.
 14. The process according to claim3, wherein in step II) one or more sequestrants are added in the aqueousphase.
 15. A process, comprising dispersing the imido-alkanpercarboxylicacid according to claim 1 in water.
 16. A process, comprising dispersingthe imido-alkanpercarboxylic acid according to claim 2 in water.